“Sleep-disordered breathing” generally refers to types of breathing disruption that occur during sleep. The most common form of sleep disordered breathing is obstructive sleep apnea (“OSA”). OSA affects approximately 20 million Americans—as many as asthma or diabetes. Less than 10% of people with OSA have been diagnosed and fewer have been treated. Loud, intermittent snoring, apneas, and hypopneas characterize OSA. Because the symptoms of sleep apnea present themselves as a result of a precursor, SDB has become the general term used to describe any disease state that manifests apneas and/or hypopneas during sleep. Apneas and hypopneas interfere with gas exchange, fragment sleep, and frequently cause oxygen desaturations. In severe cases, patients may experience these oxygen desaturations and arousals from sleep hundreds of times each night.
The most common treatment of SDB is to administer continuous positive airway pressure (CPAP). The use of nasal CPAP to treat OSA was invented by Sullivan and taught in U.S. Pat. No. 4,944,310. Briefly stated, CPAP treatment acts as a pneumatic splint of the airway by the provision of a positive pressure, usually in the range 4-20 cm H2O. The air is supplied to the airway by a motor driven blower that is coupled via an air delivery hose to a nose (or nose and/or mouth) mask sealed with the patient's face. More sophisticated forms of CPAP treatment may be provided by bi-level ventilators, proportional assist ventilators and servo-controlled ventilators. Such devices are typically used by the patient on a daily basis before and during sleep.
For example, nasal CPAP treatment of OSA may involve the use of an automated blower, such as the AUTOSET T™ device or AUTOSET SPIRIT™ available from ResMed Ltd. Examples of suitable nasal CPAP masks are the MIRAGE™ nasal mask and the MIRAGE™ full face mask also available from ResMed Ltd. The AUTOSET T™ device continuously monitors the state of the patient's airway and determines an appropriate pressure to treat the patient, increasing it or decreasing it as necessary. Alternatively, bi-level pressures are delivered to the patient as in the VPAP II™ devices also available from ResMed Ltd. Some of the principles behind the operation of the AUTOSET T™ and VPAP II™ devices are described in U.S. Pat. No. 5,704,345. The entire disclosure of U.S. Pat. No. 5,704,345 is incorporated herein by reference. Other forms of pressure treatment are available such as that which is delivered in accordance with a smooth pressure waveform template and a continuous phase variable to provide comfortable pressure support substantially in phase with the patient's respiratory cycle. The device is the subject of U.S. Pat. No. 6,532,957, the entire disclosure of which is hereby incorporated by reference.
In May 2000, a study in the New England Journal of Medicine indicated a profound link between SDB and hypertension, independent of other relevant risk factors. Hypertension as a disease has been estimated to afflict more than 25% of the population over 44 years of age. Left untreated, it leads to cardiovascular diseases such as heart attacks, stroke, coronary artery disease and heart failure. Collectively, cardiovascular disease (“CVD”) is now recognized as the major cause of death and disability in modern societies. Studies have shown that over 60% of stroke, 50% of heart failure, 35% of hypertensive and 30% of coronary artery disease patients have SDB.
In general, CVDs are diseases that have an impact on the correct functioning of the heart and blood vessels. In addition to cerebrovascular diseases (stroke), other significant CVDs include myocardial infarction (heart attack), congestive heart failure (“CHF”), transient ischaemic attacks (“TIA”) and peripheral vascular diseases, to name a few. As a whole it has been estimated that about 17 million people die of CVDs annually. Early diagnosis and treatment of CVDs can be a major factor in reducing mortality associated with CVDs.
CPAP devices have in the past been used for the treatment of SDB in CVD patients. In one such device a form of pressure treatment has been directed at treatment of cardiac failure and Cheyne-Stokes breathing. In a device designated AUTOSET CS™, also provided by ResMed Ltd., pressure support is varied in phase with patient respiration in such a manner to oppose the waxing and waning changes in patient respiration that characterize Cheyne-Stokes breathing. The device is the subject of U.S. Pat. No. 6,532,959, the entire disclosure of which is incorporated herein by reference.
As disclosed by Farrell et al. in U.S. Pat. No. 6,336,454, CPAP treatment has also been recognized as a beneficial treatment of stroke. The use of CPAP treats stroke patients by improving arterial blood oxygen levels and reducing arterial carbon dioxide levels as well as improving auto-regulation of, for example, blood pressure, cardiac output and ventilation. Improvements in morbidity, such as rate and degree of recovery of vital signs and patient stabilization in the acute phase, is an expected benefit.
Also, U.S. Pat. No. 5,794,615 teaches a system including methods and apparatus for treatment of congestive heart failure. The system involves applying separate and independent gains to flow rates of pressurized gas delivered to a patient during inspiratory and expiratory phases of a respiratory cycle. The pressure support is disclosed as reducing cardiac pre-load and after load.
In short, there are many devices that can be used for treating SDB in patients that have cardiovascular disease. Nevertheless, despite a recognized need for early treatment or diagnosis of CVD patients and a lack of complete understanding of the mechanics of these diseases, little has been done to take advantage of the patient information monitoring potential of such CPAP devices that would exploit the substantial presence of these devices in the lives of SDB patients who may also be CVD patients or potential CVD patients. In short, there exists a need to track or monitor information related to such patients that would promote early treatment and diagnosis of CVD as well as further the understanding of SDB.